Cable television (CATV) systems were initially developed to provide broadcast television content to subscriber premises over a wired connection. Early systems delivered analog television signals through a tree-and-branch coaxial cable architecture. These architectures also included numerous amplifiers, line extenders and other electronic components. CATV system operators subsequently began using hybrid fiber coaxial (HFC) networks that replaced a portion of a coaxial cable signal path with a more efficient fiber optic communication path. Typically, an HFC network uses fiber to carry signals optically from a hub or other location to optical/electrical conversion nodes (“O/E nodes”). The O/E nodes convert the optically transmitted signal to electrical signals that are transported from the O/E nodes to subscribers over coaxial cable.
Early HFC networks communicated analog NTSC signals in both the fiber and coaxial legs. Now, television has migrated to digital format. Providers, such as multiple service operators (MSOs), also employ HFC access networks to deliver high-speed data, telephony, video-on-demand (VOD) and numerous other services that rely on digital data. In effect, however, digital data is still carried over many HFC networks using analog signals. Specifically, digital data is often communicated in both the fiber and coaxial portions of an HFC network by modulating the phase and/or amplitude of a sinusoidal waveform. For example, a termination system, such as a cable modem termination system (CMTS), or other network element, may modulate digital data using quadrature amplitude modulation (QAM). This results in an analog signal in which digital data is represented by changes in the phase and/or amplitude of an analog radio frequency (RF) carrier wave. This analog signal is transmitted over the fiber portion of an HFC network by using a laser to generate that analog signal in optical form. An O/E node converts that optical analog signal to an electrical version of that signal and forwards it over the coaxial portion of the network. Ultimately, the electrical version of the modulated analog signal is received at a device in a subscriber premises and demodulated to recover digital data.